This invention relates generally to interfaces between main boards, or motherboards, and circuit cards mounted thereon and more specifically to self aligning optical interfaces for such connections. Still more particularly, the invention relates to a micro electromechanical system approach to forming such an interface, using bulk silicon micromachining technology.
Interfaces between circuit cards (or daughter boards) and main boards are known. Such interfaces typically provide frictional electro mechanical contacts for transfer of electrical signals between circuits on the two boards. With recent technological advances and miniaturization of circuit components, the amount of information which may be processed on a circuit card has increased significantly, thus increasing the bandwidth requirements for data transfer between two connected circuits.
Electromechanical interconnections of the types presently used in interfaces between circuits are limited in bandwidth, however.
Moreover, although optical interconnections are capable of increased bandwidth, such interconnections require significantly increased precision of alignment, and are expensive to manufacture.
In a separate field of endeavor, it is known to manufacture semiconductor chips by etching of silicon substrates. It is also known in the prior to use MEMS (micro electromechanical systems) technology to manufacture mechanical devices, machines, actuators and sensors. MEMS technology utilizes the known bulk silicon micromachining technology. This technology utilizes chemically etched silicon pieces, or substrates, which are typically produced from  less than 100 greater than  high quality, low defect count silicon wafers. The wafers are in turn produced from single crystal silicon ingots containing controlled concentrations of dopants. Dopant levels and types should preferably be minimized to reduce dopant induced defects in the micromachined structures.
Such technology is described in U.S. Pat. No. 5,550,088 for producing self-aligned subassemblies on an optical bench. Therein, an active optoetelectronic device is mounted on a silicon base and, by using silicon based components including a variety of etched features such as grooves, cavities and alignment detents, is self aligned with a communicating optical fiber on the same silicon base. Thus, in the prior art there are provided optoelectronic devices which are self aligned with an optical fiber on an optical bench, whereby various self aligning steps are accomplished by using fiducial features formed in the silicon.
Additionally, U.S. Pat. Nos. 5,179,609 and 5,259,054 describe uses of etched silicon substrates for completely passive alignment of an active optical device and an associated optical fiber. In such an arrangement, separate silicon substrates form structural members such as a base and a header. Therein, one substrate supports the active optical device and one (or more) substrate(s) may have a groove for holding the associated optical fiber. Such configurations may utilize detents, cavities and spheres to align and mechanically attach the two substrates.
The prior art arrangements, however, apparently are only applicable to alignment of substrates, and particularly alignment of substrates which are assembled and aligned at the time of manufacture.
Moreover, the arrangements of the prior art provide optoelectronic devices, i.e., active circuits, on micromachined silicon substrates which are aligned with each other to form a single optical device.
The prior art thus fails to provide a passive interface between two circuit devices which include electrical circuits as well as optical paths, fails to provide alignment between two optical paths of separate devices, fails to provide an optical interface between commercial devices from different manufacturers, and fails to provide an optical interface between two different circuit boards, in which the interface includes two separate passive silicon substrates mounted on the two separate circuit boards. Still more particularly, the prior art fails to provide a circuit board, which has a micromachined silicon interface component attached thereto, and which thus may be self aligned with another similarly equipped circuit board.
Additionally, the prior art fails to disclose a method for connecting a first circuit board to another circuit board which includes a step of attaching to the first circuit board a chemically etched silicon substrate having fiducial features therein. Nor does the prior art provide a method for connecting circuit boards which provides for attaching micromachined silicon substrates to each of the circuit boards, each silicon substrate having fiducial features etched therein, and by mating the two substrates to each other in a self aligning fashion. The prior art also fails to disclose a method for connecting circuit boards each having passive silicon chips mounted thereon, the chips having fiducial features etched therein, which includes a step of providing ball lenses between fiducial features of the two chips to obtain a self aligning mating of the circuit boards.
It is accordingly an object of the present invention to overcome the deficiencies of the prior art.
More specifically, it is an object of the invention to provide an improved method for forming an optical interface between a circuit card and the mainboard on which the circuit card is mounted.
It is a particular object of the invention to provide an improved method for providing a self aligning optical interface between a circuit card and a mainboard.
It is yet another object of the invention to provide a method for forming between two circuit boards a passive optical interface which utilizes micro electromechanical technology.
It is a more specific object of the invention to provide an improved optical interface between a circuit card and the mainboard on which the circuit card is mounted.
It is still a more particular object of the invention to provide an improved self aligning optical interface between a circuit card and a mainboard.
It is yet another object of the invention to provide a passive, micromachined self aligning optical interface between separate circuit devices.
It is still a further object of the invention to provide a self aligning optical interface between separate circuit devices, which includes on each of the circuit devices a silicon substrate, each substrate having at least one chemically etched aligning feature, and each having a chemically etched aligning feature for an optical fiber.
It is yet another object of the invention to provide a self aligning optical interface between separate circuit devices, which includes on each of the circuit devices a silicon substrate, each substrate having at least one chemically etched aligning feature and each having a chemically etched aligning feature for an optical fiber, and each including a ball lens.
It is still another object of the invention to provide a self aligning optical interface between separate circuit devices, which includes on each of the circuit devices a silicon substrate having at least one chemically etched aligning feature and a chemically etched aligning feature for an optical fiber, each including a ball lens, and at least one of the substrates on one of the circuit devices having a reflecting surface for changing the direction of light traveling through the optical fiber thereof.
Still another object of the invention is to provide a self aligning optical interface for aligning separate matching circuit devices, which includes on each circuit device a silicon substrate, the substrate of each circuit device having at least one chemically etched aligning cavity for matching with a corresponding chemically etched aligning cavity of the substrate of another circuit device, the cavity formed by the matched aligning cavities dimensioned for holding therein a spherical lens to align the matched devices.
It is yet another object of the invention to provide a self aligning optical interface for aligning separate matching circuit devices, which includes on each circuit device a silicon substrate, the substrate of each circuit device having at least one chemically etched aligning cavity for matching with a corresponding chemically etched aligning cavity of the substrate of another circuit device, the cavity formed by the matched aligning cavities dimensioned for holding therein a spherical lens to align the matched devices, and further including an aligning feature for aligning thereon a spherical lens for light traveling through an optical fiber associated with the circuit device, whether on the substrate or on the circuit device.
These and other objects, features and advantages of the present invention will become readily apparent to those skilled in the art from the following description and drawings, wherein there is shown and described a preferred embodiment of the invention, simply by way of illustration and not of limitation of one of the best modes (and alternative embodiments) suited to carry out the invention. The invention itself is set forth in the claims appended hereto. As will be realized upon examination of the specification and drawings and from practice of the same, the present invention is capable of still other, different, embodiments and its several details are capable of modifications in various obvious aspects, all without departing from the scope of the invention as recited in the claims. Accordingly, the drawings and the descriptions provided herein are to be regarded as illustrative in nature and not as restrictive of the invention.